synthesis, characterization and study of dielectric ... · 41.9168 0.66805077 (3,2,0) 1.153954212...

Available online at www.scholarsresearchlibrary.com

Scholars Research Library

Archives of Physics Research, 2016, 7(1):1-14

(http://scholarsresearchlibrary.com/archive.html)

ISSN 0976-0970 USA CODEN: APRRC7

1

Scholar Research Library

Synthesis, Characterization and Study of Dielectric Properties, AC

Conductivity, and Surface Morphology of Ferroelectrics Ba1-

xSrxTiO3 by Ceramic Method

Smita Patil*, R.B.Pujar, Bahubali Doddannavar

P.C. Jabin Science College, Hubli-580031, Karnataka, India

_____________________________________________________________________________________________

ABSTRACT

Ferroelectrics with general chemical formula Ba1-xSrxTiO3 (x=0.3,0.5,0.7,0.9) were synthesized by ceramic method

and characterized by X-ray diffraction, study of surface morphology by scanning electron microscopy(SEM),

porosity variation with different composition of x and same behavior is indicated by SEM micrographs. Dielectric

constant studies found with dispersion is due to Maxwell Wagner type interfacial polarization. AC conductivity

studies with frequency suggest that small poloron type of conduction mechanism.

Keywords: piezoelectric, ceramic, poloron, grain boundaries, dispersion ___________________________________________________________________________________________

INTRODUCTION

The breakthrough in the research on ferroelectric materials came in the early 1950’s with widespread use of BaTiO3

based ceramics in capacitor applications and piezoelectric transducer devices. (1) particle size and surface structure

explain the distinct properties of the ferroelectrics (2).

In the present research work

In this present work the ferroelectric Ba1-xSrxTiO3 has been synthesized with x=0.3, 0.5, 0.7, 0.9 using ceramic

method for better physical properties with high purity.

Experimental part

Precursors, BaCO3, SrCO3and TiO2in AR grade, were taken in Stoichiometry proportion for preparing 10 grams of

Ba1-XSrXTiO3with x=0.3 ,0.5, 0.7 and 0.9. The required quantities of these raw materials were mixed thoroughly

in acetone medium by milling for 3 to 4 hours to get fine powders. The ferroelectric powder was pre-sintered at

10000 C for 10 hours in an air medium to make the raw materials, if any to react partially to reduce the evolution of

gas in the final sintering process. Then the powders were pressed in to pellet by adding a drop of PVA and pressed

by KBr Press by applying a pressure of about 7 tons per square inch for 5 minutes by putting a powder of about 1gm

in a di of 1 cm in diameter. The pellets were subjected to final sintering at about 12000C and furnace cooled.

Binder addition

The calcined sample at 1200 0C was chosen and mixed with polyvinyl alcohol that acts as a binder. The role of a

binder is to provide mechanical strength to the pellets that are to be formed for sintering. Binder is made by mixing

http://www.scholarsresearchlibrary.com/

Patil S et al Archives of Physics Research, 2016, 7 (1):1-14 ______________________________________________________________________________

2


2-3% of polyvinyl alcohol in powder form with distilled water and then stirring with the help of a magnetic stirrer.

The binder vaporizes during sintering. After mixing the binder the sample is left for some time so that the mixture

dries and then grinded again.

RESULT AND CONCLUSIONS

X ray characterization

X-Ray diffraction of the sample was obtained from Indian institute of science, Bangalore. Using filtered Cu.kα,

radiation of wavelength 1.5418 A0. The interplanar distance of the cubic system was calculated by the relation

d = a/ (h2+k2+l2)1/2

Where, a = lattice constant

(h, k, l) = miller indices

While the relation calculated the lattice constant

a = λ (h2+k2+l2)/2sinθ

Where, λ = wavelength of the monochromatic X-ray used

θ = glancing angle

The diffract grams were indexed in the light of the crystal structure of natural spinel BaTiO3. The prominent line in

the diffraction pattern of spinel corresponds to (110) plane. Knowing the values of θ, λ and (hkl), lattice constant was

calculated. Knowing the value of lattice constant and miller indices, the value of interplanar distance was calculated

for other planes.

Density measurement The density and porosity were calculated as follows:

Actual density (da) = m/V

Where m= mass

V= Volume

X-Ray density (dx) = 8M/Na3

Where M- molecular weight

N- Avogadro’s number

a-lattice constant

Porosity (Pa) = (dx-da) 100 =-------

dx

Data on X-Ray Diffraction

Table 1: For X=0.3 a=8.1621A0 λ=1.5418A0

2Ө Ө Sin Ө (h k l) d (A0) Calculate d obs(A0)

22.2426 11.1213 0.192886753 (0,0,1) 3.996645638 3.99684

31.6778 15.8389 0.272933465 (1,1,0) 2.824497905 2.82463

39.0354 19.5177 0.334098047 (1,1,1) 2.307406484 2.30752

45.4871 22.74355 0.386607143 (2,0,0) 1.994013856 1.99411

51.1842 25.5921 0.431961399 (2,1,0) 1.784650207 1.178474

57.5744 28.7872 0.481557893 (2,1,1) 1.600845944 1.60092


3


66.1869 33.09345 0.54600619 (2,1,0) 1.411888755 1.41196

70.7069 35.35345 0.57861873 (1,0,3) 1.332310829 1.33238

75.3387 37.66935 0.611103692 (3,0,1) 10261488043 1.26155

79.6232 39.8116 0.640265231 (2,2,2) 1.204032271 1.20409

83.8336 41.9168 0.66805077 (3,2,0) 1.153954212 1.15305

Figure 1: X-Ray diffraction pattern for X=0.3(Ba0.7Sr0.3 TiO3)

Table 2: For X=0.5 a=8.1851A0 λ=1.5418A0


22.3469 11.17345 0.19377977 (0,0,1) 3.978227 3.97842

32.2221 16.11105 0.277499942 (1,1,0) 2.77801 2.77815

39.7956 19.8978 0.340343445 (1,1,1) 20265064923 2.26518

46.0967 23.04835 0.391507772 (2,0,0) 1.969054142 1.96915

51.3630 25.6815 0.433368116 (2,1,0) 1.778857215 1.77894

57.5845 28.79225 0.481635137 (2,1,1) 1.6005892 1.60067

66.1760 33.088 0.545926497 (2,2,0) 1.4112094858 1.41216

67.3645 33.68225 0.554586664 (3,0,1) 1.390044242 1.9011

76.8363 38.41815 0.621396005 (3,1,1) 1.240593749 1.24065

84.0062 42.0031 0.669170813 (2,2,2) 1.152022749 1.15112


4


Figure 2: X-Ray diffraction pattern for X=0.5 (Ba0.5 Sr0.5 TiO3)

Table 3: For X=0.7 a=8.1610A0 λ=1.5418A0


22.5402 11.2701 0.19543438 (0,0,1) 3.944546493 3.94474

32.2479 16.12395 0.27771624 (1,1,0) 2.775854952 2.77599

39.7798 19.8899 0.340213792 (1,1,1) 2.265928122 2.26604

46.2977 23.14885 0.393121207 (2,0,0) 1.960972812 1.96107

52.0467 26.02335 0.438737399 (2,1,0) 1.757087498 1.75717

57.5855 28.79275 0.481642785 (2,1,1) 1.600563785 1.60064

67.6035 33.80175 0.556320996 (2,2,0) 1.385710777 1.38578

76.8726 38.4363 0.621644168 (3,0,1) 1.240098499 1.24016

81.4254 40.7127 0.652266433 (2,2,2) 1.181879 1.18096


5


Figure 3: X-Ray diffraction pattern for X=0.7 (Ba0.3Sr0.7 TiO3)

Table 4: For X=0.9 a=8.1829A0 λ=1.5418A0

2Ө Ө Sin Ө (h k l) d (A0) Calculate d obs (A0)

22.6975 11.34875 0.1967820427 (0,0,1) 3.197564418 3.91775

32.3564 16.1782 0.278625711 (1,1,0) 2.76679419 2.76693

39.9131 19.95655 0.341307433 (1,1,1) 2.258667479 2.25878

46.4251 23.21255 0.394143226 (2,0,0) 1.955887982 1.95598

52.2547 26.12735 0.440367791 (2,1,0) 1.750582163 1.75067

57.7232 28.8616 0.482695532 (2,1,1) 1.597072994 1.59715

67.7425 33.87125 0.557328553 (2,2,0) 1.383205644 1.38327

72.4703 36.23515 0.591100613 (1,0,3) 1.3404177297 1.30424

77.0870 38.5435 0.623108627 (3,0,1) 1.237183961 1.23724

81.6354 40.8177 0.653654426 (3,1,1) 1.179369357 1.17845


6


Figure 4: X-Ray diffraction pattern for X=0.9 (Ba0.1 Sr0.9 TiO3)

Table 5: Data on Porosity

Composition(X) x-ray density gr/cm Actual density gr /cc Porosity

P=dx-da/dx

0.3 4.54922 2.96566 34.80%

0.5 4.3636 2.7940 38.77%

0.7 4.3560 2.14256 50.81%

0.9 4.1785 3.7918 9.254%

Figure 5: Porosity VS Composition

0.3 0.4 0.5 0.6 0.7 0.8 0.9

10

20

30

40

50

POR

OSI

TY

COMPOSITION

B


7


Table 6: Data on lattice parameters

The diffraction pattern of ferroelectrics indicates tetragonal of perovskites structure without extra peaks this confirms

the formation of single phase ferroelectrics.

The observed and estimated values of d for each plane are in good agreement with earlier reports (q) the tetragonality

ratio (c/a) is constants the variation of lattice constants with composition is listed in table no (6). From the table, it is

observed that lattice parameters decrease with increases “Sr” content it is attributed to the volume differences of Ionic

radius Sr=219pm. Ti=176pm, Ba =25pm&O=48pm ions.

Porosity Variation of porosity with composition is depicted in table (5) from the table it is noticed that porosity of all the

samples lies in the tangle of 9 to 50 it indicates that porosity increases up to x=0.7 & reaches minimum x=0.9. The

same behavior indicated by SEM Micrographs.

Experimental detail for SEM

The surface morphology of ferroelectric is carried out by scanning electron microscopy (SEM) from Indian institute

of science, Bangalore. The average grain size of ferroelectric sample the average grain size was calculated by

counting number of grain boundaries intercepted by a measured length of a random straight line drawn on

micrographs [3].

Average grain size = length / number of particles =______μm

Photo 1: X=0.3 SEM for Ba0.7Sr0.3TiO3

composition(X) lattice constant

a(A0)

C

(A0)

Tetragonality

(c/a)

0.3 3.99463 3.99463 1.001

0.5 3.92889 3.92889 1.000

0.7 3.92584 3.92584 1.000

0.9 3.91302 3.91302 1.000


8


Photo 2: X=0.5 SEM for Ba0.5Sr0.5 TiO3

Photo 3: X=0.7SEM for Ba0.3Sr0.7 TiO3

Photo 4: X=0.9 SEM for Ba0.1 Sr0.9 TiO3

Table 7: Data on Average grain size

Above tabulation indicates that, as the composition of ferroelectrics increases, the average grain size also increases.

Composition(X)BaTiO3 Average Grain Size

0.3 0.101 µm

0.5 0.214 µm

0.7 0.2303 µm

0.9 0.2283 µm


9


The SEM micrographs of ferroelectric samples with the four different compositions shown in the photos (1-4)

respectively. It is observed that all the samples show fine particles without segregation of impurity and highly dense

microstructure with the proper grain growth after sintering. The average grain size was calculated by counting number

of grain boundaries intercepted by a measured length of a random straight line drawn on micrographs [3].

Experimental detail for dielectric properties and AC conductivity

a) Dielectric constant and dielectric loss

The final sintered pellet samples were well polished and coated with silver paste on both surfaces for good ohmic

contact. This silver pasted pellet samples of ferroelectric are used to estimate the parallel capacitance (Cp) and

dielectric loss tangent (tanQ) at room temperature in the frequency range of 0 Hz to1MHz.

The dielectric constant is calculated using the relation,

ε’ = Cpt

ε0A

Where Cp - parallel capacitance,

t -thickness of the pellet,

A -cross sectional area of the pellet (πr2 = nd2 /4),

ε0-permittivity of free space = 8.854 x 10-12 F/m.

Therefore ε 1 = 4 C p t

8.854x10-12 x3.142x d2

Therefore ε1= 14.38Cpt x1012 d2

Above Equation is used to estimate dielectric constant of ferroelectric samples.

b) AC Conductivity

The AC conductivity (σac) is related to the dielectric relaxation caused by localized electric charge carriers. The

frequency dependent AC conductivity is calculated from the dielectric constant (ε’) and loss tangent (tanδ) i.e.

σac= ε’ ε0 ω tan δ

Where ε’ - the relative dielectric constant of the material,

ε0- Permittivity of free space,

tanδ - loss tangent

ω-angular frequency

The frequency response of the dielectric behavior and AC conductivity is known as relaxation spectra or dispersion

curve. This curve gives the valuable information about the type of conduction mechanism present in the polycrystalline

sintered ferroelectric samples.

RESULTS AND DISCUSSION

Dielectric constant The variation of dielectric constant with frequency of all the samples is shown in figure.6-17. The dielectric constant

decreases rapidly up to 1 kHz due to usual dielectric diversion in low frequency region. Beyond 1khg it almost remains

constant in high frequency region. The dispersion is due to Maxwell wages type interfacial polarization (4) in

agreement with Koops phenomenon magical theory (5). The maximum dielectric constant at low frequency is due to

space charge polarization at grain boundaries, interfacial dislocation pileups, oxygen. Vacancies, grain boundaries

&defects (6) for the composition X=0.7 the dielectric constant is maximum it is attributed maximum space charge

polarization at the grain boundaries. The Maximum grain size & minimum grain boundary area at X=0.7 results in the

increase of mean free path of electron & hence dielectric constant becomes maximum at X=0.7.


10


Figure 6: Dielectric constant VS Log frequency (f) for X=0.3 (Ba0.7Sr0.3TiO3)

Figure 7: Dielectric constant VS Log frequency (f) for X=0.5 (Ba0.5Sr0.5 TiO3)

Figure 8: Dielectric constant VS Log frequency (f) for X=0.7 (Ba0.3Sr0.7 TiO3)


11


Figure 9: Dielectric constant VS Log frequency (f) for X=0.9 (Ba0.1 Sr0.9 TiO3)

The graph representation loss angle (tanδ) VS Log frequency (f)

Figure 10: loss angle (tanδ) VS Log frequency (f) for X=0.3 (Ba0.7Sr0.3 TiO3)



12



Figure 13: loss angle (tanδ) VS Log frequency (f) for X=0.9 (Ba0.1 Sr0.9 TiO3)

The graph representation AC-Conductivity Slog frequency (f)

Figure 14: AC-Conductivity VS Log frequency (f) for X=0.3 (Ba0.7 Sr0.3 TiO3)


13


Figure 15: AC-Conductivity VS Log frequency (f) for X=0.5 (Ba0.5 Sr0.5 TiO3)

Figure 16: AC-Conductivity VS Log frequency (f)X=0.7 (Ba0.3 Sr0.7 TiO3)

Figure 17: AC-Conductivity VS Log frequency (f) X=0.9 (Ba0.1 Sr0.9 TiO3)

REFERENCES

1. A Safari, R K Panda, V F Janas, Ferroelectric Ceramics: Processing, Properties & Applications. 2. B Jaffe, W Cook, H Jaffe, Piezoelectric Ceramics, Academic Press, London, 1971. 3. Goel NC, thesis Delhi University, 1977. 4. CG koops, Phy Rev,1951,83,121.


14


5. AJ Bosmon, HJ VanDwal, Adv phys.

6. KW Wagner, Am J Phys, 1993,40,8176.

synthesis, characterization and study of dielectric ... · 41.9168 0.66805077 (3,2,0) 1.153954212...

Documents